This invention relates generally to a gearshift lever for automatic transmissions and more particularly to a locking device for gearshift levers that are moved through a series of positions to effect different operating and drive conditions of the automatic transmission.
The problem occurring in automobiles with automatic transmissions is the inadvertent movement of the car resulting from a driver changing the gearshift lever from the park or neutral positions to a drive position while inadvertently stepping on the gas pedal rather than the intended action of stepping on the brake pedal. It is thus desirable to provide a lockable gearshift lever in automatic transmissions that requires the driver to keep his foot on the brake pedal in order to move the gearshift lever from the park or neutral positions into a driving position.
Gearshift lever interlocks have previously been disclosed, see for example European Patent Application No. 86110975.9, publication no. 246,353. Such locking devices operate to keep the gearshift or gear selector level of an automatic transmission locked in the park (P) and neutral (N) positions, releasing the selector level only if the brake pedal is depressed or actuated. Actuation of the brake pedal energizes an electrically controlled circuit that unlocks the selector level permitting it to be shifted into one of the drive positions. The gearshift level interlock ensures that the driver is forced to locate and depress the brake pedal before placing the car in gear. This greatly reduces the possibility that the driver will mistake the accelerator pedal for the brake pedal.
In addition to controlling movement of the gearshift lever out of the park or neutral positions when the ignition is on and the motor is running, it is also desirable to control movement of the gearshift lever when the ignition is off. If the motor is not running, the car may move forward or backward if it is on an inclined surface when the gearshift lever is moved out of the park or neutral positions. Thus, it is preferable for the locking device to be operable in the locking position with the electrically controlled locking device in the deenergized state, i.e. without power. Thus, if the electrically controlled locking device is not energized, it will be engaged and the gear selector lever cannot be moved from the park position.
A disadvantage of a locking device that must be electrically activated to release the gearshift lever is that if power being supplied to the electrically controlled locking device is interrupted the vehicle can no longer be moved. This disadvantage presents a particular problem if during operation of the vehicle the gearshift lever becomes locked in the neutral position. This situation may arise if, for example, the vehicle is to be backed up and the gearshift lever is moved from one of the drive positions through neutral and into reverse. If power to the locking device is interrupted and cannot be electrically disabled, the car would be locked in neutral when the gearshift lever is passed through this position.
An alternative method for locking the gearshift lever is to provide an electrically activated locking device that locks the lever in response to a continuous electrical signal and unlocks the lever when electrical power is removed. However such a method is not effective when the ignition is off because the electrical power of the battery is insufficient to meet the power consumption needs of the electrical locking device.
It is therefore an object of the present invention to provide a locking device for the gearshift lever of an automatic transmission that effectively locks the gearshift lever in the park and neutral positions, that consumes a minimum of electric power, and that is operable even if the power to the electrically controlled locking device is interrupted. In summary, the locking device of the present invention is configured such that the gearshift lever is unlocked from the park (P) position when electrical power is supplied to the locking device, while the gearshift lever is unlocked from the neutral (N) position when electrical power is removed from the locking device. The present invention utilizes a conventional control unit, described for example in the previously mentioned European Patent Application No. 86110975.9, that monitors contacts associated with the N and P positions and the brake pedal. If the brake pedal is actuated or depressed, the control unit causes the locking device to be electrically energized to release the gearshift lever when it is in the P position and the control unit operates to remove electrical power from the locking device to release the gearshift lever from the N position. Any simple electrical circuit or control unit such as that described in the above mentioned European patent application is suitable for the present invention. It does not form an important aspect of the present invention and is not described in any detail herein.
The locking device of the present invention can comprise, for example, a pin that can be introduced into the path of movement of the gearshift lever. An electromagnet can be utilized, for example, to move the pin into an extended position in the path of the gearshift lever and a withdrawn position out of the path of the gearshift lever. The extended position can be effected by electrically energizing the electromagnet.
In one embodiment, when the gearshift lever is in the N position an opening in the interlock element of the locking device is aligned with the pin of the electromagnet. If the pin is extended, the lever is locked in the N position. If the pin is permanently withdrawn in the event of an inoperable electromagnet or due to power interruption, it cannot be introduced into the opening of the interlock element and thus the gearshift lever cannot be locked in the N position.
Extension of the pin of the electromagnet has an opposite effect on the gearshift lever when in the P position. When in the P position, the gearshift lever is locked by means of a catch which comes to rest against a corresponding stop. When the brake pedal is actuated, the pin is moved to its extended position out of the electromagnet displacing the catch and moving it into a position which is not in contact with the stop. The gearshift lever can then be moved out of the P position.
As a backup to the electromagnet, i.e. in case of an electromagnet malfunction, a manually operable unlocking device may be provided to displace the catch and permit the gearshift lever to be moved from the P position. If the electromagnet is not functioning or cannot be energized and the pin remains retracted, the gearshift lever will not be locked in the N position and can be unlocked from the P position by means of the manual unlocking device. Further, in order to prevent the electromagnet from being continually energized with its pin extended and locking the gearshift lever in the N position, the manually operable unlocking device can be devised to interrupt power to the electromagnet thereby releasing the gearshift lever from the N position. If the manually operated device for interrupting power to the electromagnet is designed as a temporary or intermittent pushbutton, then the manual unlocking device must be actuated each time the lever is returned to the N position, assuming that the electromagnet is constantly energized. As an alternate arrangement, the manual unlocking device may be designed to permanently disable power supply to the electromagnet. However, this will prevent the brake-dependent gearshift lever interlock system from being operable in the N position.